var, let, const

JavaScript allows you to declare variables using three keywords: var, let, and const.

1. var:

  • It’s function-scoped, meaning the variable is accessible throughout the function in which it’s declared.
  • Variables declared with var can be re-declared and updated.

Example:

JavaScript
var age = 25;
var age = 30;  // Re-declaration is allowed
age = 35;  // Update is allowed

2. let:

  • Introduced in ES6, it’s block-scoped, meaning the variable is only accessible within the block ({}) in which it is declared.
  • Variables declared with let can be updated but cannot be re-declared within the same block.

Example:

JavaScript
let age = 25;
age = 30;  // Update is allowed

3. const:

  • Also block-scoped like let, but once a value is assigned to a const variable, it cannot be reassigned. It must be initialized at the time of declaration.

Example:

JavaScript
const age = 25;
// age = 30; // This will throw an error
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